The Toxic Planet was a planet in the Pegasus galaxy, which provided safe refuge for the Lost Tribe. It is unlikely the planet possessed a Stargate as the Lost Tribe only uses their ships for travel.
History
Following the Lost Tribe's defeat and destruction of their intergalactic ships in the first battle with the Wraith, they abandoned their settlements and made their way to the Toxic planet. There, they could hide from the Wraith, who could not follow them and finish the pursuit.
For the next 10,000 years, the Lost tribe was able to live on this world wearing only simple breathing apparatus. It is likely they rebuilt much of their technology in that time period in order to adapt to their new surroundings, likely their ships and Armored exoskeletons were invented in this time frame. The planet likely possessed moderate levels of resources, enough to build interstellar spacecraft, but not enough to reconstruct any intergalactic vessels.
Though over time the atmosphere of the planet became steadily worse, the Lost Tribe in return replaced the now ineffective breathing apparatuses with their Battle Armor suits, though even this measure failed to completely resolve the problem. As a result, the Lost Tribe was forced to venture for the first time in 10,000 years, into a Wraith dominated galaxy. During their travels, they came across the Attero Device, discovered its purpose, and eventually activated it with the help of Doctors McKay and Jackson, though unfortunately for the Lost Tribe the device was destroyed. (SGA: "The Lost Tribe")